The present invention relates to the "hairpin" lacing process portion of the manufacture of heat exchangers and an apparatus used for automatic hairpin lacing. In particular it relates to the apparatus and process of automatically drawing/inserting copper or aluminum or other suitable material cooling tubes through a stack of thin, pliable aluminum fins which have been punched for receiving said cooling tubes.
Heat exchangers have many uses in industry and commerce. Large numbers of them are used in the automotive industry for radiators, oil coolers, and air conditioning heat exchangers.
The generally accepted construction for such heat exchangers includes a plurality of spaced, parallel, longitudinally extending first fluid carrying tubes. A plurality of spaced, heat transfer "fins" are mounted on these fluid carrying tubes and are surrounded by a second fluid medium.
With automotive heat exchangers, the first fluid carrying tubes are generally of copper or aluminum or other suitable material and the heat transfer fins are soft, pliable, and thin aluminum sheet material.
The manufacturing process for such heat exchangers has been automated to some extent. However, one portion of this manufacturing process which has remained manual, and therefore labor intensive and slow, has been the lacing of the heat exchanger tubes through holes punched through the fins.
Efforts have been partially made to automate the assembly process for these heat exchangers. In this regard, a plurality of fins are cut and assembled into a "stack". This stack is then machine punched for the intended pattern of the tubes.
As the tubes are to serpentine back and forth through the fin stack, assembly has been further partially automated by first joining pairs of parallel extending tubes with elbows (return tubes) to form a "hairpin". These hairpins are then gently inserted through an adjacent pair of holes in the fin stack by an assembly operator.
After all of the tubes have been inserted through the fin stack, from a first side of the stack, the hairpin tubes are expanded to fit tightly within the fin stack and the opposite side return bends are connected to the tubes.
Previous attempts to automate hairpin lacing have proved unsuccessful as there has been no apparatus developed which can lace the tubes through the punched holes in the stack of fragile fins without either elongating the punched holes or bending or otherwise distorting the fins.
It is necessary to draw the tubes through the fins in a noise and vibration empounded environment without distorting the fins or the punched holes therethrough, beyond the tolerances specified for the expanding apparatus, which later expands the tubes to fit tightly against the fins.
It is desirable to provide an uncomplicated, reliable, accurate apparatus for automatically drawing the heat exchanger hairpins through the prepunched holes of a fin stack.